Based on our previous clinical findings on the Imaging and Phase I study using mAb B3 radiolabeled with 111In and 90Y we have designed a follow up study of 90Y- B3 with autologous stem cell support for patients with metastatic breast carcinoma. The primary objectives of this study are to determine the dose-limiting toxicities and the maximum tolerated dose of 90Y-B3 when administered with stem cell support. 70 % of breast carcinomas express the B3 antigen. Secondary objectives are to evaluate the anti-tumor activity and the immunogenicity of this agent when given in marrow ablative doses. The study has been recently approved by the NCI Protocol Review and Monitoring Committee and should be open for accrual soon.